Median and Mode

/**
 * Fintech Math Bootcamp · Lesson 034 of 120
 * Median and Mode
 * Module 04: Location, Ranking, and Exploratory Summaries
 *
 * Scenario: A typical settlement delay by order and frequency
 * Rule:     median = middle order statistic; mode = most frequent value
 *
 * Try it:   Does an unchanged median prove no customer had a severe delay?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

export function lesson034() {
  const x = [1, 2, 2, 4, 9].sort((a,b) => a-b);
  const mid = Math.floor(x.length / 2);
  const median = x.length % 2 ? x[mid] : (x[mid-1] + x[mid]) / 2;
  const counts = new Map<number, number>();
  for (const v of x) counts.set(v, (counts.get(v) ?? 0) + 1);
  const maxCount = Math.max(...counts.values());
  const modes = [...counts].filter(([,n]) => n===maxCount).map(([v]) => v);
  const result = {median, modes};
  return result;
}

export const checkedResult = {"median":2,"modes":[2]};

// Run this file directly: npx tsx lessons/04-location-ranking-and-exploratory-summaries/034-median-and-mode.ts
if (process.argv[1] && import.meta.url.endsWith(process.argv[1].replace(/\\/g, "/").split("/").pop()!)) {
  console.log(JSON.stringify(lesson034(), null, 2));
}

# Fintech Math Bootcamp · Lesson 034 of 120
# Median and Mode
# Module 04: Location, Ranking, and Exploratory Summaries
#
# Scenario: A typical settlement delay by order and frequency
# Rule:     median = middle order statistic; mode = most frequent value
#
# Try it:   Does an unchanged median prove no customer had a severe delay?
#
# Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
# Free course:    https://courses.thefintechbuilder.com
# Synthetic teaching example, not financial advice or a production library.

import json


def lesson034() -> dict:
    x = sorted([1, 2, 2, 4, 9])
    mid = len(x) // 2
    median = x[mid] if len(x) % 2 else (x[mid - 1] + x[mid]) / 2
    counts: dict[float, int] = {}
    for v in x:
        counts[v] = counts.get(v, 0) + 1
    max_count = max(counts.values())
    modes = [v for v, n in counts.items() if n == max_count]
    return {"median": median, "modes": modes}


if __name__ == "__main__":
    print(json.dumps(lesson034(), indent=2))

/**
 * Fintech Math Bootcamp · Lesson 034 of 120
 * Median and Mode
 * Module 04: Location, Ranking, and Exploratory Summaries
 *
 * Scenario: A typical settlement delay by order and frequency
 * Rule:     median = middle order statistic; mode = most frequent value
 *
 * Try it:   Does an unchanged median prove no customer had a severe delay?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class Main {
    static Map<String, Object> lesson034() {
        double[] x = {1, 2, 2, 4, 9};
        Arrays.sort(x);
        int mid = x.length / 2;
        double median = x.length % 2 == 1 ? x[mid] : (x[mid - 1] + x[mid]) / 2;

        Map<Double, Integer> counts = new LinkedHashMap<Double, Integer>();
        for (double v : x) {
            Integer seen = counts.get(v);
            counts.put(v, seen == null ? 1 : seen + 1);
        }
        int maxCount = Collections.max(counts.values());
        List<Double> modes = new ArrayList<Double>();
        for (Map.Entry<Double, Integer> entry : counts.entrySet()) {
            if (entry.getValue() == maxCount) modes.add(entry.getKey());
        }

        Map<String, Object> result = new LinkedHashMap<String, Object>();
        result.put("median", median);
        result.put("modes", modes);
        return result;
    }

    public static void main(String[] args) {
        System.out.println(toJson(lesson034(), ""));
    }

    // --- Minimal JSON printer: maps keep insertion order, 2-space indent. ---

    static String toJson(Object value, String indent) {
        if (value == null) return "null";
        if (value instanceof String) return "\"" + value + "\"";
        if (value instanceof Double) return formatNumber((Double) value);
        if (value instanceof Number) return value.toString();
        if (value instanceof double[]) {
            List<Object> items = new ArrayList<Object>();
            for (double v : (double[]) value) items.add(v);
            return toJson(items, indent);
        }
        String inner = indent + "  ";
        StringBuilder sb = new StringBuilder();
        if (value instanceof Map) {
            Map<?, ?> map = (Map<?, ?>) value;
            if (map.isEmpty()) return "{}";
            sb.append("{\n");
            int i = 0;
            for (Map.Entry<?, ?> entry : map.entrySet()) {
                sb.append(inner).append('"').append(entry.getKey()).append("\": ")
                  .append(toJson(entry.getValue(), inner))
                  .append(++i < map.size() ? ",\n" : "\n");
            }
            return sb.append(indent).append('}').toString();
        }
        List<?> list = (List<?>) value;
        if (list.isEmpty()) return "[]";
        sb.append("[\n");
        for (int i = 0; i < list.size(); i++) {
            sb.append(inner).append(toJson(list.get(i), inner))
              .append(i + 1 < list.size() ? ",\n" : "\n");
        }
        return sb.append(indent).append(']').toString();
    }

    static String formatNumber(double v) {
        if (Double.isNaN(v) || Double.isInfinite(v)) return "null";
        if (v == Math.rint(v) && Math.abs(v) < 1e15) return Long.toString((long) v);
        return Double.toString(v);
    }
}

// Fintech Math Bootcamp · Lesson 034 of 120
// Median and Mode
// Module 04: Location, Ranking, and Exploratory Summaries
//
// Scenario: A typical settlement delay by order and frequency
// Rule:     median = middle order statistic; mode = most frequent value
//
// Try it:   Does an unchanged median prove no customer had a severe delay?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.

package main

import (
	"encoding/json"
	"fmt"
	"sort"
)

// Location holds the middle order statistic and every most-frequent value.
type Location struct {
	Median float64   `json:"median"`
	Modes  []float64 `json:"modes"`
}

func lesson034() Location {
	x := []float64{1, 2, 2, 4, 9}
	sort.Float64s(x)
	mid := len(x) / 2
	var median float64
	if len(x)%2 == 1 {
		median = x[mid]
	} else {
		median = (x[mid-1] + x[mid]) / 2
	}

	// Count each value, remembering the order values first appear.
	counts := map[float64]int{}
	var order []float64
	for _, v := range x {
		if counts[v] == 0 {
			order = append(order, v)
		}
		counts[v]++
	}
	maxCount := 0
	for _, n := range counts {
		maxCount = max(maxCount, n)
	}
	modes := []float64{}
	for _, v := range order {
		if counts[v] == maxCount {
			modes = append(modes, v)
		}
	}
	return Location{Median: median, Modes: modes}
}

func main() {
	out, _ := json.MarshalIndent(lesson034(), "", "  ")
	fmt.Println(string(out))
}

/**
 * Fintech Math Bootcamp · Lesson 034 of 120
 * Median and Mode
 * Module 04: Location, Ranking, and Exploratory Summaries
 *
 * Scenario: A typical settlement delay by order and frequency
 * Rule:     median = middle order statistic; mode = most frequent value
 *
 * Try it:   Does an unchanged median prove no customer had a severe delay?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

#include <algorithm>
#include <charconv>
#include <cmath>
#include <iostream>
#include <string>
#include <utility>
#include <vector>

// --- Minimal JSON value and printer: objects keep insertion order, 2-space indent. ---

struct Json {
    enum class Kind { Null, Number, Text, Array, Object };
    Kind kind = Kind::Null;
    double number = 0;
    std::string text;
    std::vector<std::string> keys;  // object keys, parallel to items
    std::vector<Json> items;        // array elements or object values
};

Json num(double v) { Json j; j.kind = Json::Kind::Number; j.number = v; return j; }
Json str(const std::string& s) { Json j; j.kind = Json::Kind::Text; j.text = s; return j; }
Json arr(const std::vector<Json>& values) { Json j; j.kind = Json::Kind::Array; j.items = values; return j; }

Json arr(const std::vector<double>& values) {
    std::vector<Json> items;
    for (double v : values) items.push_back(num(v));
    return arr(items);
}

Json obj(const std::vector<std::pair<std::string, Json>>& fields) {
    Json j;
    j.kind = Json::Kind::Object;
    for (const auto& [key, value] : fields) { j.keys.push_back(key); j.items.push_back(value); }
    return j;
}

std::string formatNumber(double v) {
    if (!std::isfinite(v)) return "null";
    char buf[64];
    auto end = std::to_chars(buf, buf + sizeof buf, v).ptr;  // shortest round-trip form
    return std::string(buf, end);
}

void writeJson(std::ostream& out, const Json& j, const std::string& indent) {
    switch (j.kind) {
    case Json::Kind::Null: out << "null"; return;
    case Json::Kind::Number: out << formatNumber(j.number); return;
    case Json::Kind::Text: out << '"' << j.text << '"'; return;
    default: break;
    }
    bool isObject = j.kind == Json::Kind::Object;
    if (j.items.empty()) { out << (isObject ? "{}" : "[]"); return; }
    std::string inner = indent + "  ";
    out << (isObject ? "{\n" : "[\n");
    for (size_t i = 0; i < j.items.size(); ++i) {
        out << inner;
        if (isObject) out << '"' << j.keys[i] << "\": ";
        writeJson(out, j.items[i], inner);
        out << (i + 1 < j.items.size() ? ",\n" : "\n");
    }
    out << indent << (isObject ? '}' : ']');
}

// --- Lesson ---

Json lesson034() {
    std::vector<double> x = {1, 2, 2, 4, 9};
    std::sort(x.begin(), x.end());
    size_t mid = x.size() / 2;
    double median = x.size() % 2 ? x[mid] : (x[mid - 1] + x[mid]) / 2;

    // Count each value in first-seen order.
    std::vector<std::pair<double, int>> counts;
    for (double v : x) {
        auto it = std::find_if(counts.begin(), counts.end(), [v](const auto& c) { return c.first == v; });
        if (it == counts.end()) counts.push_back({v, 1});
        else ++it->second;
    }
    int maxCount = 0;
    for (const auto& c : counts) maxCount = std::max(maxCount, c.second);
    std::vector<double> modes;
    for (const auto& c : counts) {
        if (c.second == maxCount) modes.push_back(c.first);
    }
    return obj({{"median", num(median)}, {"modes", arr(modes)}});
}

int main() {
    writeJson(std::cout, lesson034(), "");
    std::cout << '\n';
}

// Fintech Math Bootcamp · Lesson 034 of 120
// Median and Mode
// Module 04: Location, Ranking, and Exploratory Summaries
//
// Scenario: A typical settlement delay by order and frequency
// Rule:     median = middle order statistic; mode = most frequent value
//
// Try it:   Does an unchanged median prove no customer had a severe delay?
//
// Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
// Free course:    https://courses.thefintechbuilder.com
// Synthetic teaching example, not financial advice or a production library.

// --- Minimal JSON value and printer: objects keep insertion order, 2-space indent. ---

#[allow(dead_code)]
enum Json {
    Null,
    Num(f64),
    Str(String),
    Arr(Vec<Json>),
    Obj(Vec<(String, Json)>),
}

#[allow(dead_code)]
fn nums(values: &[f64]) -> Json {
    Json::Arr(values.iter().map(|&v| Json::Num(v)).collect())
}

#[allow(dead_code)]
fn obj(fields: Vec<(&str, Json)>) -> Json {
    Json::Obj(fields.into_iter().map(|(k, v)| (k.to_string(), v)).collect())
}

fn format_number(v: f64) -> String {
    if !v.is_finite() {
        return "null".to_string();
    }
    if v.fract() == 0.0 && v.abs() < 1e15 {
        return format!("{}", v as i64);
    }
    format!("{:?}", v) // shortest round-trip form
}

impl Json {
    fn render(&self, indent: &str) -> String {
        let inner = format!("{}  ", indent);
        match self {
            Json::Null => "null".to_string(),
            Json::Num(v) => format_number(*v),
            Json::Str(s) => format!("\"{}\"", s),
            Json::Arr(items) if items.is_empty() => "[]".to_string(),
            Json::Obj(fields) if fields.is_empty() => "{}".to_string(),
            Json::Arr(items) => {
                let lines: Vec<String> = items.iter().map(|v| format!("{}{}", inner, v.render(&inner))).collect();
                format!("[\n{}\n{}]", lines.join(",\n"), indent)
            }
            Json::Obj(fields) => {
                let lines: Vec<String> = fields
                    .iter()
                    .map(|(k, v)| format!("{}\"{}\": {}", inner, k, v.render(&inner)))
                    .collect();
                format!("{{\n{}\n{}}}", lines.join(",\n"), indent)
            }
        }
    }
}

// --- Lesson ---

fn lesson034() -> Json {
    let mut x: Vec<f64> = vec![1.0, 2.0, 2.0, 4.0, 9.0];
    x.sort_by(|a, b| a.partial_cmp(b).unwrap());
    let mid = x.len() / 2;
    let median = if x.len() % 2 == 1 { x[mid] } else { (x[mid - 1] + x[mid]) / 2.0 };

    // Count each value in first-seen order.
    let mut counts: Vec<(f64, usize)> = Vec::new();
    for &v in &x {
        match counts.iter_mut().find(|(value, _)| *value == v) {
            Some((_, n)) => *n += 1,
            None => counts.push((v, 1)),
        }
    }
    let max_count = counts.iter().map(|&(_, n)| n).max().unwrap_or(0);
    let modes: Vec<f64> = counts.iter().filter(|&&(_, n)| n == max_count).map(|&(v, _)| v).collect();
    obj(vec![("median", Json::Num(median)), ("modes", nums(&modes))])
}

fn main() {
    println!("{}", lesson034().render(""));
}

/**
 * Fintech Math Bootcamp · Lesson 034 of 120
 * Median and Mode
 * Module 04: Location, Ranking, and Exploratory Summaries
 *
 * Scenario: A typical settlement delay by order and frequency
 * Rule:     median = middle order statistic; mode = most frequent value
 *
 * Try it:   Does an unchanged median prove no customer had a severe delay?
 *
 * Lesson article: https://thefintechbuilder.com/financial-mathematics-statistics-and-data-foundations/location-ranking-and-exploratory-summaries/median-and-mode/
 * Free course:    https://courses.thefintechbuilder.com
 * Synthetic teaching example, not financial advice or a production library.
 */

using System;
using System.Linq;
using System.Text.Json;

var options = new JsonSerializerOptions { WriteIndented = true };
Console.WriteLine(JsonSerializer.Serialize(Lesson034(), options));

static object Lesson034()
{
    double[] x = new double[] { 1, 2, 2, 4, 9 }.OrderBy(v => v).ToArray();
    int mid = x.Length / 2;
    double median = x.Length % 2 == 1 ? x[mid] : (x[mid - 1] + x[mid]) / 2;
    var counts = x.GroupBy(v => v).Select(g => new { value = g.Key, count = g.Count() }).ToList();
    int maxCount = counts.Max(c => c.count);
    double[] modes = counts.Where(c => c.count == maxCount).Select(c => c.value).ToArray();
    return new { median, modes };
}